A pregnancy that goes beyond 40 weeks is described as overdue, or post dates. Being overdue is common (especially in a first pregnancy) and, apart from the discomfort of being heavily pregnant, does not usually pose problems.
There is a small but significant increase in stillbirths in pregnancies that continue longer than 42 weeks, although the numbers remain low, and is also slightly more common in mothers aged 40 and above. The reasons for this are not fully known, but it is likely that the placenta becomes less efficient at nutrient and oxygen transfer. If you have not given birth by 40+12 weeks, you will therefore be offered an induction of labour to avoid problems of placental insufficiency.
Discussion about possible induction should take place at about 37–38 weeks. At around 40 weeks your midwife will re-check your estimated delivery date using your dating scan measurements. She may also do an internal examination to ascertain how ‘ripe’ (ready) the cervix is and may, after discussion with you, do a ‘sweep’ of the membranes around the baby at the top of the cervix. This means stretching the internal cervical opening with her finger to encourage the release of prostaglandins and uterine tightenings.
While it is known to reduce the need for induction with drugs, if you prefer not to have the procedure, you will agree a date to start the induction process, usually between 4012 weeks.
You may, of course, decline induction and wait for labour to begin naturally, in which case you will be offered daily monitoring after 42 weeks with CTG (though, again, you are free to decline). Bear in mind, however, that no amount of monitoring can predict whether your placenta might cease to function adequately just a few hours after an assessment, potentially putting your baby in danger.
You might prefer to have a Caesarean section rather than an induction, and you should discuss with your obstetrician the pros and cons of this method of delivery, which will depend on factors such as whether you have had a previous vaginal delivery.
This is an edited extract from One Born Every Minute: Expecting a Baby? by Dr Penelope Law (Quadrille, £25).
Text © 2013 Dr Penelope Law